Ultrasound transducers are finding wide applications such as sensors for motion and presence detection. An ultrasound transducer is a device that converts electrical energy into mechanical energy. Most often, the term ultrasound transducer is used for referring to piezoelectric transducers that convert electrical energy via piezoelectricity into ultrasound. Piezoelectric crystals and piezoelectric ceramics have the property of changing size when an electrical signal is applied, thus applying an alternating electrical signal causes them to oscillate. The resonance frequency of the devices is dependent on the dimensions and the build-up of device. Since piezoelectric crystals or ceramics generate an electrical signal when a mechanical force is applied to them, the same crystal or ceramic can be used as an ultrasound transmitter and as an ultrasound receiver.
WO 2009/004558 describes a transducer where a membrane is formed over a front substrate, and a piezoelectric layer is formed over the membrane at an active portion and peripheral portions located adjacent the active portion. A patterned conductive layer including first and second electrodes is formed over the piezoelectric layer. Further, a back substrate structure is provided having supports located at the peripheral portions adjacent the active portion. The height of the supports is greater than a combined height of the patterned piezoelectric layer and the patterned conductive layer. Many transducers may be connected to form an array.